1. Field of the Invention
The present invention relates to an electrode plate, a wound electrode group (electrode assembly) using the electrode plate, and a cylindrical battery.
2. Description of the Related Art
An example of conventional negative electrode plates is configured by applying a negative electrode active material onto a base member formed of a punching steel plate. This negative electrode plate is wound via a separator together with a positive electrode plate and has an outermost peripheral portion positioned on the outermost periphery of an electrode assembly.
Conventionally, in order to enhance the mechanical strength of an outermost peripheral portion, the rate of hole area of a base member within a predetermined range from a winding terminal end of the outermost peripheral portion may be set to be smaller than those of other portions, as disclosed in JP-A-2004-247221.
However, with the above configuration, the winding terminal end of the outermost peripheral portion or a winding terminal end of a positive electrode plate is brought into contact with a portion having a large rate of hole area at the base member of a negative electrode plate. When a winding terminal end of a negative or positive electrode plate located on the outermost periphery is pressed inward in a radial direction in a case where, for example, a winding roller pressurizes an electrode assembly in fabricating the electrode assembly, the winding terminal end bites the negative electrode plate with which the winding terminal end is brought into contact, thereby raising a problem that the base member of the negative electrode plate is broken.
In JP-A-2005-56674, a negative electrode plate includes a main body wound inside of an electrode assembly, an outermost peripheral portion wound around the outermost periphery of the electrode assembly, and a boundary portion formed between the main body and the outermost peripheral portion. In the wound electrode assembly, the rate of hole area of the base member that forms the boundary portion of the negative electrode plate is set to be smaller than those of other portions, thereby preventing any occurrence of a crack or the like on the boundary portion.
JP-A-2005-56674 discloses the configuration having the reduced rate of hole area at the boundary portion, which is located at a position circumferentially different from the winding terminal end of the positive electrode plate and the winding terminal end of the negative electrode plate. Therefore, as described above, the winding terminal end of the negative electrode plate or the winding terminal end of the positive electrode plate bites a portion having a large rate of hole area at the base member of the negative electrode plate, thereby raising a problem of breakage of the base member of the negative electrode plate.